Overall Stability Research Of Steel I-beams Under Combined Bending And Torsion

The stability of thin-walled steel beams is often a decisive role to their carrying capacity, and it's an important aspect in structure design. Steel beams are often suffering combined bending and torsion as the influence of eccentric load in actual projects. In our country, the method to calculate the overall stability of simply supported beams under concentrated load, uniformly distributed load or fixed end moment is introduced in Code for design of steel structures (GB 50017-2003). But there are not any relevant rules for calculating the overall stability of steel beams under combined bending and torsion in this code. Technical code of cold-formed thin-wall steel structures (GB 50018-2002) has introduced the method to calculate the overall stability of cold-formed thin-wall steel beams under bending and torsion, but it's only suitable for the cold-formed thin-wall steel structures. Nowadays, the research on the overall stability of steel I-beams under combined bending and torsion is steel rare. So, it's necessary to research the overall stability of steel I-beams under combined bending and torsion. It has some scientific research meaning and applied value.In this paper, it presents the overall stability factors of steel I-beams under three typical loads by using energy method firstly. The formulas for calculating the overall stability of simply supported steel I-beams under three eccentric loads is proposed in combination with the formulas for calculating the overall stability of cold-formed thin-wall steel beams under bending and torsion while loads on the compression flange or the tension flange. The loads include uniformly distributed eccentric load, concentrated eccentric load in the midspan and concentrated eccentric load in one-third and two-thirds of the span. The paper uses finite element software ANSYS to analyze the overall stability of steel I-beams under combined bending and torsion according to different parameters, such as section dimension, span, load type, load bias and load eccentricity. The section shapes include doubly symmetric I-section and monosymmetric I-section with compression flange enhanced or tension flange enhanced. It has calculated one hundred and eithty models in all. We can check and evaluate the theoretical formulas in elastic range or elastoplastic range by comparing finite element results with theoretical results. And it studies the influence to the overall stability of simply supported I-beams under combined bending and torsion while torsional moment, load bias, section dimensions and span vary.